Researchers in Finland have examined how different food processing methods affect the biochemical composition of plant-based food products, suggesting that current processing classification systems are limited.
The research team at Finland’s University of Turku analysed various commercially available plant-based products, such as foods made from soya, peas, wheat and fava beans. Using a non-targeted metabolomics analysis, the researchers showed that different processing methods have significant effects on the products’ biochemical compositions.
Plant-based products, such as meat substitutes, are often processed using different methods to improve their nutritional or organoleptic quality.
The category has faced criticism due to many plant-based alternatives falling under the ‘ultra-processed food’ (UPF) umbrella – however, the researchers emphasised that not all plant-based products are the same when it comes to health and nutrition, with many plant-based products that fall into the UPF category still containing high levels of potentially beneficial compounds found in the unprocessed plant.
Kati Hanhineva, professor of food development at the University of Turku, said: “Plants and plant-based products are known to contain phytochemicals, which are bioactive compounds that can have health benefits. Phytochemicals are a very large group of different compounds found only in plants, of which there are thousands of different types.”
She explained that while on average, we consume 0.5-1g of phytochemicals per day depending on our diet, research into how different food processing methods impact these compounds has been limited thus far.
The researchers’ study focused in particular on soya-based products and their isoflavonoids. Products prepared using protein concentrates or isolates, such as plant-based burger steaks, contained very little isoflavonoids. In contrast, products made using lighter processing techniques, such as soya chunks and tofu, still contained a high level of isoflavonoids from the original soya bean.
Jasmin Raita, doctoral researcher at the university, explained that fermentation was highlighted as an important processing method in the results.
“We found that in tempeh, for example, these isoflavonoids were in a form that is more readily absorbed due to the activity of the microbes used in fermentation,” she commented. Tempeh is a protein-rich food originating from Indonesia, usually made by fermenting soya using starter cultures.
When the researchers used existing processing classification systems for the studied plant-based products, some of the fermented tempeh products fell into the ultra-processed category typically considered harmful, as did products made with extrusion technology, even though these still contained high levels of isoflavonoids.
With this considered, Raita said it is important to note that food processing “should not be seen as exclusively harmful,” with fermentation as an example of a method offering nutritional benefits to the product.
Ville Koistinen, university research fellow, said: “Processing food is common, and even unprocessed food is often eventually processed at home, for example by cooking. Classification systems primarily take into account the processing technique used for the product and the type and number of added ingredients, rather than the biochemical composition of the product.”
“It cannot be assumed that all processing makes a product unhealthy, because ultimately it is only the nutritional components of the edible product that matter, and how they are absorbed by our bodies. These determine the nutritional value and healthiness of food products.”
While the phytochemicals in the compounds identified in the study may have health benefits, they are not currently included in the nutrition labelling of food products. Hanhineva explained that these phytochemicals could also indicate how well the original composition of the plant-based raw material has been preserved.
“If there are no phytochemicals left in the product, it indicates that the product has undergone heavy industrial processing, after which the biochemical composition is completely different to that of the original plant used as a raw material,” she added. “This perspective is not fully supported by current food processing classification systems.”
The researchers call for future food classifications to be developed, taking into account the effects of processing on the biochemical composition of products. They noted that this future classification should acknowledge the loss of useful compounds in the process and the formation of new ones, as well as the value of added ingredients to the product – not just the addition of harmful ingredients such as salt. For example, many spices are rich in compounds with health benefits.
Hanhineva commented: “Highly processed plant-based protein-rich foods have been on the market for such a short time that it is too early to say anything for certain about the healthiness of all processed plant-based products as a whole, but research on this topic is active”.
“What is known, however, is that in population-based epidemiological studies, all food groups rich in phytochemicals are healthy, while unhealthy food categories typically do not contain them. Therefore, it is justified that the range of phytochemicals should be better recognised in the categorisation of foods.”
